FeLV is a common infection of domestic cats throughout the world and a cause of significant morbidity and mortality. The prevalence of antigenaemia may vary from 1 to 5 per cent in healthy cats to 15 to 30 per cent in sick cats (Hosie M. J. et al., Veterinary Records, 1989, 128, 293-297; Braley J., Feline Practice, 1994, 22, 25-29; Malik R. et al., Australian Veterinary Journal, 1997, 75, 323-327; Arjona A. et al., Journal of Clinical Microbiology, 2000, 38, 3448-3449). The virus may establish a life-long infection characterized by a persistent viraemia and a fatal outcome. Most FeLV-related diseases occur in persistently infected animals, and they are always serious and mostly fatal. Among the most frequently diagnosed conditions are lymphomas, myeloid leukaemias, immunodeficiency and non-regenerative anaemia. The infection can be controlled by the identification and isolation of persistently viraemic cats, which are the source of the infection, and vaccines have also helped to prevent the virus spreading. Several FeLV vaccines are available; most of them contain either inactivated virus or recombinant subunits. Their efficacy is controversial (Sparkes A. H., Journal of Small Animal Practice, 1997, 38, 187-194). Vaccine breakdowns have been observed and there is a need for an improvement in efficacy and particularly for more evidence of protection in field conditions. An alternative way would be to use recombinant viral vector. The canarypox virus vector and especially the ALVAC vector have been tested for the expression of FeLV genes (Tartaglia J. et al., Journal of Virology, 1993, 67, 2370-2375; Poulet H. et al., Veterinary Record, 2003, 153, 141-145). A commercial recombinant FeLV vaccine is also available (EURIFEL® FeLV, Merial).
There is thus a general need for an improvement in efficacy and safety of the FeLV vaccines.
Generally the efficacy of a vaccine is increased by the administration of a higher dose of immunogens, or by the formulation of the vaccine with adjuvants, or a combination of both.
The administration of a higher dose of immunogens increases dramatically the cost of the vaccine in such a manner that the vaccine becomes too expensive for customers.
In the other way, the formulation of the vaccine with adjuvants renders the vaccine more efficacious and allows sometime to reduce the amount of immunogens. However adjuvanted vaccines induce a higher rate of local adverse reactions than non-adjuvanted ones (Gobar et al., JAVMA, 2002, 220(10), 1477-1482) and thereby increase the risk of vaccine-associated fibrosarcomas at the injection site (Baker R. J., Feline Practice, 1998, 26(5), 18-20).
It has also been proposed to use needle-free injectors in veterinary field (WO-A-98/03659; WO-A-92/15330; WO-A-98/03658; van Rooij et al., Vet. Immunol. Immunopathol., 1998, 66(2), 113-126; U.S. Pat. No. 6,451,770; Schrijver et al., Vaccine, 1998, 16(2-3), 130-134). There are however contradictory results in the art (McKercher P. D. et al., Can. J. Comp. Med., 1976, 40, 67-74; Epstein, Hum. Gene Ther., 2002, 13(13), 275-280; Haensler, Vaccine, 1999, 17(7-8), 628-638).
Citation or identification of any document in this application is not an admission that such document is available as prior art to the present invention.